The present invention broadly relates to needle localization, for example, insertion of a tip of a hypodermic needle to a required location in an animal such as a human being under treatment and, more particularly relates to a needle configured to be accurately guided using ultrasound, an ultrasound imaging system including the needle and method of guiding the needle using the ultrasound imaging system.
Ultrasound is used with increasing frequency to image body parts both to obtain diagnostic information, as well as an adjunct to help guide needle placement for a variety of reasons. For example, ultrasound is often used to help guide a needle tip to an area to deposit medication. The area of interest where the needle tip will traverse or ultimately lie is often around important vascular and nervous tissue that could easily be damaged or disrupted should the needle tip inadvertently pierce the structure. Because of this and several other reasons, it is imperative that the operator know the exact location of the needle tip at all times. However, with current ultrasound imaging systems and technology, visualizing the needle tip at all times is difficult and problematic.
An ultrasound machine or system that can be used to visualize tissue includes a transducer that contains an array of piezo-electrical crystals. As a pulsed current is applied to the piezoelectric crystals, pulsed ultrasonic phonons (packet of sound in the ultrasonic frequency) are generated that radiate from the transducer face and travel through the medium of interest. In this way, the ultrasound transducer operates as a transmitter. The ultrasound transducer also operates as a receiver to receive transmitted ultrasound energy reflected back by the different parts of medium of interest. A piezoelectric crystal (with similar characteristics to the transmitter piezoelectric crystal), that detects the sound energy produced by the transmitter responds to the energy by vibrating. The ultrasound transducer may include piezoelectric crystals dedicated to transmission and piezoelectric crystals dedicated to receiving, or may rely on the same piezoelectric crystals to both transmit and receive. In that case, after the crystals emit ultrasound energy in a transmission phase, there is a quiet or listening phase. That is, the ultrasound energy travels through the tissue and some of ultrasound energy is reflected (echo) off the tissue based on differences of tissue density and returns back to the “listening” crystals (pulse-echo cycle). As the crystals in the receive mode absorb the reflected, diffracted and/or diffused ultrasound energy, they vibrate creating a voltage or current signal with the magnitude that correlates to the strength of the returned reflected ultrasound energy. Using a signal processor (CPU), the return signals are processed and a two dimensional (2D) ultrasound image is rendered. Using a linear array of crystals and sweeping excitation pulse across this array to generate an array of transmitted ultrasound signals (FIG. 1A), linear spatial resolution can be determined. Using time delay and amplitude, the depth and contrast if the tissue medium is produced (FIG. 1B). With these pieces of information (see target and needle in FIG. 2A for a simple example of a reflected only signal), the CPU can convert the echoes (i.e., signal representative of the reflected ultrasound energy) into a 2D image that represents the tissue structures and a needle within the tissue (FIG. 2B).
Many of the structures that need to be accessed with a needle are such that the angle between transducer face and the needle is large, for example, greater than 30 degrees. With an increasing angle between the transducer face and needle (see FIG. 3), a decrease in the amount of reflected ultrasound energy is received or detected at the transducer making visualization very difficult. In addition, if the needle is below a strong reflecting surface, the needle becomes invisible.